The present invention generally relates to intravascular catheters. Specifically, the present invention relates to intravascular balloon catheters such as single lumen balloon-tipped micro catheters.
Intravascular balloon catheters are used is a wide variety of medical procedures to diagnose and treat vascular abnormalities such as aneurysms, stenotic lesions, intracranial shunts, etc. Such balloon catheters may be used for purposes of dilation, occlusion, flow control or tissue reformation.
Intravascular balloon catheters are typically navigated through the vasculature to the desired treatment site using a guide wire. The guide wire is insertable into the catheter and may be torqued to steer the distal end thereof and thereby direct the catheter into the desired vascular passage. Once in the desired position, the balloon may be inflated to treat the vascular abnormality. Such balloon catheters usually include a guide wire lumen to accommodate the guide wire in addition to a separate inflation lumen for inflating and deflating the balloon.
The provision of a guide wire lumen separate from an inflation lumen dictates a catheter profile that may be too large for accessing relatively narrow vasculature often encountered, for example, in cranial applications. Accordingly, it is desirable to provide a combined guide wire lumen and inflation lumen to reduce the profile of the catheter and thereby enable access to narrow vasculature. Balloon catheters incorporating a combined guide wire lumen and inflation lumen are often referred to as xe2x80x9cinnerlessxe2x80x9d or xe2x80x9csingle lumenxe2x80x9d balloon catheters.
A single lumen balloon catheter requires some sort of seal or valve between the guide wire and the catheter distal of the inflatable balloon. Examples of such a catheter construction may be found in U.S. Pat. No. 5,776,099 to Tremulis and commonly assigned U.S. Pat. No. 4,813,934 to Engelson et al. The seal is typically provided adjacent the distal end of the balloon and forms a close fit or an interference fit with the guide wire. Because of the close fit or interference fit, some friction between the guide wire and the seal may be encountered.
Due to the friction between the guide wire and the seal, in addition to the friction between the balloon and the vasculature, the balloon may be susceptible to longitudinal collapse. The tendency for longitudinal collapse is exasperated by the balloon structure which is usually formed of a thin flexible material.
To address the potential for longitudinal collapse, a support coil may be provided extending from the proximal end of the balloon to the distal end of the balloon adjacent the seal. The support coil provides column strength to the balloon and reduces the potential for longitudinal collapse. Examples of such support coils may be found in Engelson ""934 and in Tremulis ""099. The commercial embodiment of the Tremulis ""099 catheter included a polymer tube in the support coil.
Although the support coil provides column strength to the balloon, the transition in flexibility from the shaft immediately proximal to the balloon to the support coil within the balloon may be fairly abrupt. The support coil is inherently flexible and the balloon is very flexible since it is formed of a thin pliable material. The shaft, by contrast, is usually less flexible to provide sufficient pushability. The result is an abrupt transition in stiffness from the relatively less flexible distal shaft portion to the relatively more flexible support coil and balloon. An abrupt transition in stiffness may translate into reduced trackability and an increased potential for kinking.
The present invention overcomes these disadvantages by providing a unique single lumen balloon-tipped micro catheter wherein the distal portion of the shaft is reinforced and extends into the balloon to eliminate abrupt transitions in stiffness in the balloon region. The result is a micro catheter exhibiting superior pushability, trackability, and kink resistance.
In an exemplary embodiment, the micro catheter includes an elongate shaft having a distal portion comprising a reinforcement layer disposed between two polymer layers. The elongate shaft also includes a lumen extending therethrough to accommodate a removable guide wire and to define an inflation lumen. An inflatable balloon is connected to the distal portion of the shaft such that the distal portion of the shaft extends into the interior of the balloon to thereby eliminate significant transitions in stiffness. One or more inflation ports extend through the distal portion of the shaft to provide a fluid path between the lumen of the shaft and the interior of the balloon. A seal is connected to the distal portion of the shaft distal of the inflation port to provide a fluid tight seal about a guide wire such that the balloon may be inflated via the lumen of the shaft.
The reinforcement layer in the distal portion of the shaft may comprise a braided tubular structure to impart enhanced pushability and kink resistance without compromising flexibility. With a braid reinforcement layer, the inflation ports are preferably disposed between the filaments of the braid to avoid compromising the mechanical integrity of the distal portion of the shaft. The filaments of the braid may be formed of a super elastic metal such as a nickel titanium alloy to withstand significant strains often encountered in tortuous vasculature.
One or more radiopaque marker bands may be disposed between the inner and outer polymer layers adjacent the balloon to facilitate fluoroscopic visualization. The outer surface of the catheter shaft may include a lubricious coating thereon to reduce friction between the catheter and the vasculature as the catheter is navigated therethrough. The entire outer surface of the shaft may be coated except at locations where the balloon is bonded to avoid jeopardizing bond integrity. This may be accomplished by utilizing a masking technique during the coating process.
The seal may be formed by a reduced diameter portion of the distal portion of the shaft. Preferably, the seal is sized to form an interference fit with the guide wire. The seal may be formed of a non-elastomer polymer, but operate within the elastic region of the material. Operating within the elastic region of the material allows the seal to be. formed of any suitable plastics without requiring that the material be elastomeric.
The balloon may be formed of a thermoplastic polyisoprene rubber such as hydrogenated polyisoprene, which has superior functional properties in addition to desirable manufacturing characteristics. The thermoplastic polyisoprene rubber balloon material may be utilized in a wide variety of balloon catheters, in addition to the single lumen balloon-tipped micro catheter of the present invention.